This invention relates to position and attitude measurement in general, and more particularly to an improved method and apparatus for measuring the relative position and attitude of one body with respect to another.
For example, at the present time, the position and attitude of six degree of freedom (6 DOF) motion bases used in flight simulation are determined from measured leg extensions using equations that are essentially the inverse of those used in driving the legs. This determination is less credible than an independent determination. One reason is that, if a leg or leg attachment fails, the measured leg extension on such a leg may be within acceptable limits of the commanded leg extension. Therefore, such a platform failure would not be sensed by a system which determines platform position and attitude from measured leg extensions. A second reason is that any error in the basic equations used to determine commanded leg extensions from a desired 6 DOF motion base position and attitude would be reflected in the inverse solution. This is, of course, a consequence of a non-independent measurement.
There have been other systems developed in the past utilizing light or sound energy for determining distance and position. One simple example of this is the Polaroid cameras which utilize ultrasound for determining distances for taking photographs. Another example is the system disclosed in U.S. Pat. No. 3,352,223 in which three lasers are utilized to determine the attitude and altitude of an instrumented aerospace vehicle with respect to an uninstrumented planetary or lunar surface. This device permits only obtaining pitch and roll angles but not the heading or the azimuth of the vehicle and the local vertical distance or altitude but not the latitude and longitude, or the coordinates of the point on the surface directly below the vehicle and from which the local vertical distance is measured.
Thus, the use of beams of electromagnetic energy to determine distance has been used in the past and is still finding applications.
An article, starting on page 69 of the Mar. 1, 1982 issue of Aviation Week and Space Technology entitled: "USAF Seeks Increased Robot Precision", describes a device for positioning the end effector of a robot with respect to its target on a workpiece for the purpose of issuing corrective commands to the robot's controller. This device uses a "coarse vision sensor consisting of one General Electric 2200 binary camera and a Digital Equipment Corp. 11/03 minicomputer" as a coarse sensor and "a fine resolution system comprising three General Electric 2200 cameras, each resolving a 1 sq. in. area, and a Motorola 6800 minicomputer."
Ultrasonic ranging systems, per se, are available, for example, from the Polaroid Corporation, Ultrasonic Components Group. These operate over distances up to 35 feet. However, such systems have not been applied in apparatus such as motion systems and the like.
Thus, there is a need to independently determine the relative position and attitude of one body with respect to another in all six degrees of freedom (three in translation and three in rotation) that exist between two bodies.
In particular, there is a need to independently measure the relative position and attitude of 6 DOF flight simulation motion bases.